1. Field of the Invention
The present invention relates to an electronic package for integrated circuits. .
2. Description of Related Art
Integrated circuits (ICs) are typically housed within a package that can be mounted to a printed circuit board. A conventional IC package includes an outer housing that encapsulates the integrated circuit and a lead frame that couples the circuit to the printed circuit board. The outer housing is typically constructed from a dielectric material such as a glass filled epoxy. Glass filled epoxies have a relatively low coefficient of thermal conductivity. Consequently a substantial portion of the heat generated by the integrated circuit is transferred to the printed circuit board through the lead frame. The leads of the lead frame are relatively long and create a thermal resistance that may cause excessive junction temperatures in the IC. High junction temperatures may damage or otherwise effect the performance of the circuit.
To improve thermal efficiency, some package designs employ a heat slug that is coupled to the integrated circuit and the housing. The heat slug is typically mounted to the integrated circuit and provides a direct thermal path between the IC and the housing. To assemble such a package, the heat slug is initially coupled to the integrated circuit and encapsulated by an uncured silica filled epoxy. The epoxy is then heated and cured to create a rugged outer housing.
Although heat slugs improve the thermal efficiency of the package, the outer housing material still creates a significant thermal impedance. It would be desirable to have a heat sink which has a surface exposed to the ambient to increase the thermal efficiency of the electronic package it would also be desirable to have a heat sink, that extends from the circuit die to the top surface of the package, is rigidly attached to the housing and which does not allow moisture to migrate into the die cavity.